A 3D Printed NARAM

[vcp]

I just attended NARAM-60, which was the first competition of any kind that I'd attended in over 30 years. I haven't even flown a rocket in that time. I expected to be pretty much 'out of it' as far as competition goes (largely correct), so I set another personal goal. I've been 3D printing for the past ~6 years, so I wanted to determine if 3D printed models could be competitive in the performance events (i.e., other than scale bits). So, I printed models for just about every event. I had several good flights, but my inexperience showed in the areas of pistons, altimeters, and cluster ignition.

Never-the-less, my models were mostly different, and I thought the community might be interested in seeing what can be done. As I get the models and posts prepared, and perhaps after a bit more testing, I'll be posting links to them here. The full models themselves will be posted on Thingiverse.

The model that did the best was my C Egglofter. It's 100% printed in ABS, with a dry weight of 21.8 grams. With a few changes I expect I can get that to less than 20 grams. The full story on it is on Thingiverse here: https://www.thingiverse.com/thing:3056609

 

[Leo]

Very nicely done!

I am going to try to attend NARAM 61. I'll be designing my own version. We should then do a competition among 3D printed models

 

[vcp]

I'll be very interested to see your models Leo. Even though I posted my model with pretty explicit instructions, I really don't expect many people to try to print an exact copy - it's intended more to be an inspiration and proof-of-concept. I expect there will be a trickle, then a wave of printed models in competition. Good luck at it.

 

[Leo]

Do you want to set some guidelines for the 3D printed egglofter?

e.g:
1. Min overall length in mm
2. Min inside payload diameter in mm
3. The model must be completely made of 3D printed parts only
4. The use of any other materials such as paper, metals, tape is not permitted
5. An elastic shock is permitted
6. Shock cord / anchors of nylon or kevlar material is permitted
7. A parachute made of any material is permitted
8. The model may only be flown on Estes "C" type engines (18mm)
9. No electronics of any kind is permitted
10. The model must make 3 successful flights without any form of repairs between the flights
11. The same egg must be used for all 3 flights
12. After the 3rd flight the egg must be in tack
12. ???

 

[vcp]

I've just posted my NARAM-60 printed Payload Altitude model to Thingiverse here: https://www.thingiverse.com/thing:3061709

 

[Leo]

You do not mention the vent holes for the altimeter on Thingiverse. Could it be that you forgot them?

Are you interested in some guidelines for 3D printed egglofters?

 

[vcp]

You do not mention the vent holes for the altimeter on Thingiverse. Could it be that you forgot them?

Are you interested in some guidelines for 3D printed egglofters?

Not forgotten. Read many varying opinions on their necessity, and went with the thought that since it was open at altitude, a vent wouldn't be necessary. Seemed to work on the egglofter, I believe the payloader had premature launch detect because I prepped it long before launch, so I don't know if a vent would have helped. On my SuperRoc flight, I did add a vent, and got the same apparent premature launch detect. There were apparently a lot of those with the MicroPeaks - better prep procedures and protection from light presumably will help. I don't have enough experience flying them to know.

I hadn't seen any egglofter in the flesh in over 30 years, and wasn't aware of any other printed ones, so I'm all ears.

 

[Leo]

The vent holes, preferably 3 evenly placed around the body tube, are necessary. Without the vent holes the altimeter will not register a change in pressure and therefore will not know that the rocket has lifted off. Use 1.5 to 2 mm holes for your application.
Use black filament next time you print the section that houses the altimeter. This is to shield it from light as that can cause incorrect sensor readings.

 

[Alan15578]

Gary,
Congratulations on your 3D printed egglofter and your 2nd Place NARAM finish. It looks good and has a shape that no one could mistake for a rolled paper construction.

You mentioned a "dry weight" of 21.8 grams. Could you put that figure in context? For example, what was the comparable weight of your last old school C EL model, of the weight of current competitive non printed NARAM C EL rockets? Does the printing offer lower weight models with the same strength and durability, or just freedom of shape and uniqueness? FWIW, I have not competed in many years, although you have me beat on the absence record. My Eggloft preference was based on the old CMR Humpty Dumpty; I just stretched out the motor mount tube to a longer length. The egg is placed in a plastic bag and tied off with the shock cord. The egg is held in the nose cone with just a coupling ring and a bit of padding. That alone could save you a couple grams. On the other hand, I like that you designed in a pocket to hold the altimeter. I've dabbled a bit with vacuum forming, and I could reboot that, but honestly I think fiberglass is the lighter way to go. Still, if you are just going for minimum mass, it is hard to beat the strength and stability of simple cones and cylinders.

The main reason that I am responding is that you said you spent hundreds of CFD hours devising the airframe shape. I hope most of that was just time spent climbing the learning curve. I don't really care about the CFD engine, but I would like to know the criteria and methodology that you used. Did you impose any constraints such as length or usable parachute volume?

Since about 1990, I've had the technology to design laminar flow minimum drag bodies of revolution. I actually had the CFD portion running on a Commodore 64, but completing the optimization would have taken more computing power. I actually had the notion of designing a generic FAI fat roc body, except that I have no interest in such. FAI competition started off fine, then some time after 1980 they decided that model rockets were too hard to track, so they arbitrarily decreed that models had to be big and fat. Later they abandoned all optical tracking and went to altimeters only, but they foolishly kept the big fat rockets. The current FAI models and competition have little or no relevance to common rocketry, but they have posed an esoteric problem that may lend itself to CFD analysis. I've probably said too much, but I would like t know more about how you applied CFD in your egglofter desgn.

Alan Jones